Who among us hasn’t come back from a shopping excursion, looked over the just-purchased haul, and wondered, What was I thinking? Often, our shopping decisions aren’t the result of a completely logical thought process, but are instead affected by what we smell, hear, and touch, and what people around us are doing inside the store.

In the nearly 20 years that I’ve been interviewing shoppers, it’s clear that most consumers like to think of themselves as rational, in-control human beings who carefully weigh costs versus benefits, compare prices, and rarely buy on impulse or come home with more than they need. It’s also clear that few, if any, among us make wholly rational decisions when shopping.

Most consumers are oblivious to the fact that when you’re shopping, you’re the subject of a multi-pronged sensory campaign. Retailers, on the other hand, are well aware of how environmental cues—smells, sounds, colors, and more—can influence consumers’ moods, desires, and willingness to spend money.

With the year’s busiest shopping period at hand, it’s a good time to try to understand how our senses and emotions can be manipulated inside stores, sometimes to the point that we’re not thinking straight.

Scents
Smells make a direct hit to emotional centers of our brain. They have a unique ability to evoke moods and memories. It’s no surprise that Bloomingdale’s, Jimmy Choo, Hugo Boss, Victoria’s Secret, and scores of other retailers use scents to stimulate positive and associative moods and enhance our perception of their brands and products.

Studies show that the right scent can increase our perception of the quality of products and brands. Certain smells—for instance, leather, lemon, vanilla, and baby powder in a shoe store—are also known to get people to stay out shopping longer.

Pine, that quintessential holiday scent, can evoke a feeling happiness, earthy wholesomeness, and nostalgia. It’s just the right mix to get early holiday shoppers in the mood to buy. Another holiday favorite smell, peppermint, increases physiological arousal and engagement and heightens alertness among shoppers.

Music
Traditional seasonal favorites like “Have Yourself a Merry Little Christmas” get people into the holiday spirit, which for most consumers includes an association with spending and generosity. More importantly, classic holiday music evokes nostalgia. Recent research shows that nostalgia elevates positive moods and helps people feel better about themselves. They feel more connected to others and sense more continuity and meaning in their lives.

Nostalgia powerfully evokes the past in a rosy haze. Particularly in uncertain economic times, nostalgia transports people from the present back to a time that felt more understandable, more familiar and within one’s control. After all, no matter what your past was like, you know what happened next—and that makes life feel more certain. Being eased into a sense of comfort and warmth is a recipe for increased spending on gifts in stores.

Colors
Colors create more than a scene. They’re loaded with symbolic associations and influence our moods and perceptions. Red and green are the predominant colors of the season, and while each affect us in different ways, both can push us to spend more, and spend in curious ways, over the holidays.

Red stimulates and energizes — even our spending. Waitresses wearing red have reported receiving 14% to 26% higher tips than waitresses wearing any other color uniform. Another study found that shoppers on eBay bid more aggressively for products if they’re shown against red rather than blue backgrounds.

Green, on the other hand, is an optimistic color associated with luck and wealth. It’s also been shown to have a positive effect on creativity—a possible explanation for some of the more unusual gifts found under the tree on Christmas morning.

Touch
Because we’re significantly more likely to buy what we touch, retailers carefully design stores with roadblocks and tactile displays that encourage shoppers to handle the merchandise. Recent studies show that what we’re touching can even alter our decisions regarding completely unrelated financial matters. For example, in one experiment people who held a warm pad invested 43% more money than those holding a cold pad.

Our eyes are naturally drawn toward the center of displays, where retailers often place the priciest items. The second most alluring placement is just to the right of center, the spot where right-handed people are most likely to grab first. A smart shopper will also look down, up, and to the left, to make sure all options are considered before making a purchasing decision.

Crowds & Competition
A shopper named Jeannie seemed out of breath when I spoke with her recently at an outlet mall. “I think I’m kind of hyped up,” she said. “There are so many people here and so many bargains. I feel like I’m going to miss out or that they’ll get the deal before me.” Jeannie was able to articulate what many feel when they’re shopping during the holidays: pressure, competition, anxiety. These emotions cause our bodies to react, usually in ways that interfere with calm decision-making.

Every marital therapist will tell couples to wait until they’re calm before discussing a hot-button issue. Why? When people are worked up, they tend to overreact and later regret what they’ve done. The same mechanisms are in play when shopping under pressure, often with a similar result. Over-the-top purchasing, or just plain foolish purchasing, is usually followed with buyer’s remorse. Whether it’s the stress of crowds, time pressures, fears of missing out or physical exhaustion and thirst — we all think less clearly when our hearts start racing.

Kit Yarrow chairs the psychology department of Golden Gate University and was named as the university’s 2012 Outstanding Scholar for her research in consumer behavior. She is co-author of Gen BuYand is a frequent speaker on topics related to consumer psychology and Generation Y.